The patent document P 200102902, by the same applicant, discloses a procedure for welding the layers forming a multi-layer printed circuit and a machine therefore. Essentially, the machine described in this document comprises one or more induction devices, each of which is made up of a generally U-shaped magnetic circuit wherein an inductor winding is arranged, the ends of the arms of the magnetic circuit being provided with one respective induction electrode and both electrodes being arranged perpendicularly as regards the multi-layer printed circuit to be welded, coaxially to one another, and capable of movement in both directions, the multi-layer printed circuit to be welded being arranged between both induction electrodes.
Induction electrodes are of a material with high magnetic permeability, preferably ferrite, and have a relatively high mass as regards the mass of the welding zone of the multi-layer printed circuit. During the welding of the printed circuit, the induction electrodes of each induction device, which exert pressure on the upper and lower sides respectively of the printed circuit, act as cooling elements of the welding zone they are in contact with; when the welding of the printed circuit is carried out, this causes a thermal imbalance between the layers of the printed circuit in contact with the induction electrodes and the innermost layers thereof, due to the action of the heat evacuation of the welding zone caused by the metallic mass of the induction electrodes, which under certain circumstances, can affect the welding of the printed circuit.
One solution to the problem that cooling of the welding zone creates consists of increasing the welding time, but this causes the innermost layers to overheat, with detrimental effects. Another solution consists of inserting a laminate of thermally insulating material between the end of each induction electrode and the corresponding outer layer of the printed circuit, but this gives rise to the use of additional elements in the welding process and to high preparation times.